Allow citus_*_size on index related to a distributed table

[c2main]

I just enhanced the existing code to check if the relation is an index belonging to a distributed table.
If so the shardId is appended to relation (index) name and the *_size function are executed as before.

There is a change in an extern function:
extern StringInfo GenerateSizeQueryOnMultiplePlacements(...)
It's possible to create a new function and deprecate this one later if compatibility is an issue.

Fixes #6496.

DESCRIPTION: Allows using Citus size functions on distributed tables indexes.

[c2main]

@c2main please read the following Contributor License Agreement(CLA). If you agree with the CLA, please reply with the following information.

@microsoft-github-policy-service agree [company="{your company}"]

Options:

• (default - no company specified) I have sole ownership of intellectual property rights to my Submissions and I am not making Submissions in the course of work for my employer.

@microsoft-github-policy-service agree

• (when company given) I am making Submissions in the course of work for my employer (or my employer has intellectual property rights in my Submissions by contract or applicable law). I have permission from my employer to make Submissions and enter into this Agreement on behalf of my employer. By signing below, the defined term “You” includes me and my employer.

@microsoft-github-policy-service agree company="Microsoft"

Contributor License Agreement

Contribution License Agreement

This Contribution License Agreement (“Agreement”) is agreed to by the party signing below (“You”), and conveys certain license rights to Microsoft Corporation and its affiliates (“Microsoft”) for Your contributions to Microsoft open source projects. This Agreement is effective as of the latest signature date below.

1. **Definitions**.
   **“Code”** means the computer software code, whether in human-readable or machine-executable form,
   that is delivered by You to Microsoft under this Agreement.
   **“Project”** means any of the projects owned or managed by Microsoft and offered under a license
   approved by the Open Source Initiative ([www.opensource.org](http://www.opensource.org)).
   **“Submit”** is the act of uploading, submitting, transmitting, or distributing code or other content to any
   Project, including but not limited to communication on electronic mailing lists, source code control
   systems, and issue tracking systems that are managed by, or on behalf of, the Project for the purpose of
   discussing and improving that Project, but excluding communication that is conspicuously marked or
   otherwise designated in writing by You as “Not a Submission.”
   **“Submission”** means the Code and any other copyrightable material Submitted by You, including any
   associated comments and documentation.

2. **Your Submission**. You must agree to the terms of this Agreement before making a Submission to any
   Project. This Agreement covers any and all Submissions that You, now or in the future (except as
   described in Section 4 below), Submit to any Project.

3. **Originality of Work**. You represent that each of Your Submissions is entirely Your original work.
   Should You wish to Submit materials that are not Your original work, You may Submit them separately
   to the Project if You (a) retain all copyright and license information that was in the materials as You
   received them, (b) in the description accompanying Your Submission, include the phrase “Submission
   containing materials of a third party:” followed by the names of the third party and any licenses or other
   restrictions of which You are aware, and (c) follow any other instructions in the Project’s written
   guidelines concerning Submissions.

4. **Your Employer**. References to “employer” in this Agreement include Your employer or anyone else
   for whom You are acting in making Your Submission, e.g. as a contractor, vendor, or agent. If Your
   Submission is made in the course of Your work for an employer or Your employer has intellectual
   property rights in Your Submission by contract or applicable law, You must secure permission from Your
   employer to make the Submission before signing this Agreement. In that case, the term “You” in this
   Agreement will refer to You and the employer collectively. If You change employers in the future and
   desire to Submit additional Submissions for the new employer, then You agree to sign a new Agreement
   and secure permission from the new employer before Submitting those Submissions.

5. **Licenses**.


* **Copyright License**. You grant Microsoft, and those who receive the Submission directly or
  indirectly from Microsoft, a perpetual, worldwide, non-exclusive, royalty-free, irrevocable license in the
  Submission to reproduce, prepare derivative works of, publicly display, publicly perform, and distribute
  the Submission and such derivative works, and to sublicense any or all of the foregoing rights to third
  parties.

* **Patent License**. You grant Microsoft, and those who receive the Submission directly or
  indirectly from Microsoft, a perpetual, worldwide, non-exclusive, royalty-free, irrevocable license under
  Your patent claims that are necessarily infringed by the Submission or the combination of the
  Submission with the Project to which it was Submitted to make, have made, use, offer to sell, sell and
  import or otherwise dispose of the Submission alone or with the Project.

* **Other Rights Reserved**. Each party reserves all rights not expressly granted in this Agreement.
  No additional licenses or rights whatsoever (including, without limitation, any implied licenses) are
  granted by implication, exhaustion, estoppel or otherwise.


6. **Representations and Warranties**. You represent that You are legally entitled to grant the above
   licenses. You represent that each of Your Submissions is entirely Your original work (except as You may
   have disclosed under Section 3). You represent that You have secured permission from Your employer to
   make the Submission in cases where Your Submission is made in the course of Your work for Your
   employer or Your employer has intellectual property rights in Your Submission by contract or applicable
   law. If You are signing this Agreement on behalf of Your employer, You represent and warrant that You
   have the necessary authority to bind the listed employer to the obligations contained in this Agreement.
   You are not expected to provide support for Your Submission, unless You choose to do so. UNLESS
   REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING, AND EXCEPT FOR THE WARRANTIES
   EXPRESSLY STATED IN SECTIONS 3, 4, AND 6, THE SUBMISSION PROVIDED UNDER THIS AGREEMENT IS
   PROVIDED WITHOUT WARRANTY OF ANY KIND, INCLUDING, BUT NOT LIMITED TO, ANY WARRANTY OF
   NONINFRINGEMENT, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE.

7. **Notice to Microsoft**. You agree to notify Microsoft in writing of any facts or circumstances of which
   You later become aware that would make Your representations in this Agreement inaccurate in any
   respect.

8. **Information about Submissions**. You agree that contributions to Projects and information about
   contributions may be maintained indefinitely and disclosed publicly, including Your name and other
   information that You submit with Your Submission.

9. **Governing Law/Jurisdiction**. This Agreement is governed by the laws of the State of Washington, and
   the parties consent to exclusive jurisdiction and venue in the federal courts sitting in King County,
   Washington, unless no federal subject matter jurisdiction exists, in which case the parties consent to
   exclusive jurisdiction and venue in the Superior Court of King County, Washington. The parties waive all
   defenses of lack of personal jurisdiction and forum non-conveniens.

10. **Entire Agreement/Assignment**. This Agreement is the entire agreement between the parties, and
    supersedes any and all prior agreements, understandings or communications, written or oral, between
    the parties relating to the subject matter hereof. This Agreement may be assigned by Microsoft.

@microsoft-github-policy-service agree company="Data Bene"

[onurctirtir]

Hey @c2main, thank you for the contribution.

I pushed my suggestions into a separate branch on top of your commits: f81823d.

It mostly involves some style changes but more importantly, removes the following block:

	/*	
	 * After this point, we don't need to keep relationId pointing to the table.	
	 * So we swap with indexId if relevant, only for error log...	
	 */	
	if (indexId != InvalidOid)	
	{	
		relationId = indexId;	
	}

Because I don't think we need to refer distributed table in the error messages that follows this block earlier.

[c2main]

Hey @onurctirtir

I pushed my suggestions into a separate branch on top of your commits: f81823d.

Thank you for your review and suggestions.

It mostly involves some style changes but more importantly, removes the following block:

	/*	
	 * After this point, we don't need to keep relationId pointing to the table.	
	 * So we swap with indexId if relevant, only for error log...	
	 */	
	if (indexId != InvalidOid)	
	{	
		relationId = indexId;	
	}

Because I don't think we need to refer distributed table in the error messages that follows this block earlier.

Yeah, I was unsure where to do the indexId/relationId dance. Adding the get_rel_relkind() down in the code is a good idea too.
It looks better this way.

[onurctirtir]

Hey @onurctirtir

I pushed my suggestions into a separate branch on top of your commits: f81823d.

Thank you for your review and suggestions.

It mostly involves some style changes but more importantly, removes the following block:

	/*	
	 * After this point, we don't need to keep relationId pointing to the table.	
	 * So we swap with indexId if relevant, only for error log...	
	 */	
	if (indexId != InvalidOid)	
	{	
		relationId = indexId;	
	}

Because I don't think we need to refer distributed table in the error messages that follows this block earlier.

Yeah, I was unsure where to do the indexId/relationId dance. Adding the get_rel_relkind() down in the code is a good idea too. It looks better this way.

Do you mind applying the suggested changes from mentioned commit?

[c2main]

Hey @onurctirtir

I pushed my suggestions into a separate branch on top of your commits: f81823d.

Do you mind applying the suggested changes from mentioned commit?

Well, I have looked a bit further the code and would like to propose some improvements:

• there is code duplication with shared_transfer.c, remove the duplicate
• there is an error handling which is pushed down the function calls when we may just return null and let the caller evaluate if NULL is a failure or not.
• en passant, adding pg_indexes_size() which is of interest here (tempted by other database, toast and column size but over a decade apparently no one required them)
• maybe have a more generic way to handle aggregation (sum) of remote function calls. This is cosmetic as I don't know if there is usage for that in other places of Citus code ?

The current fix is working. Improvements can be done in another PR if it's better ?

To get an idea of possible future code:

Datum
citus_relation_size(PG_FUNCTION_ARGS)
{
	CheckCitusVersion(ERROR);
        /* Ensure we have no multi-shard modification. FIXME original comment and code are not clear here */
	ErrorIfNotXactForSize();

	Oid relationId = PG_GETARG_OID(0);
	SizeQueryType sizeQueryType = RELATION_SIZE;
	uint64 size;

	/*
	 * We open the relation (table or index, probably).
	 * and release only when we're done.
	 */
	Relation relation = citus_try_relation_open(relationId, AccessShareLock);

	if (relation == NULL)
		PG_RETURN_NULL();

	size = SumDistributedSizeFunction(relation, sizeQueryType);

	if (size == NULL)
		PG_RETURN_NULL();

	relation_close(relation, AccessShareLock);

	PG_RETURN_INT64(size);
}

[c2main]

@onurctirtir I have cherry-pick your patch and moved down some code. Should be ok now.

[c2main]

Just noticed #6607 about citus size function improvements, for another PR.

[onurctirtir]

Shared comments from my (probably) last iteration.

It's hard to make flaky-test detection job passing, so I'll take care of this after this PR becomes fully ready again.

Thank you for your contribution!

[onurctirtir]

Please re-request review when this is the case, thanks.

[c2main]

@onurctirtir I believe I applied all suggested changes.

[codecov]

Codecov Report

Merging #7271 (3939682) into main (83e3fb8) will decrease coverage by 3.66%.
Report is 4 commits behind head on main.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##             main    #7271      +/-   ##
==========================================
- Coverage   93.22%   89.56%   -3.66%     
==========================================
  Files         275      275              
  Lines       59527    59588      +61     
  Branches        0     7425    +7425     
==========================================
- Hits        55495    53371    -2124     
- Misses       4032     4089      +57     
- Partials        0     2128    +2128